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clk: fix set_rate_range when current rate is out of range 

Calling clk_core_set_rate() with core->req_rate is basically a no-op
because of the early bail-out mechanism.

This may leave the clock in inconsistent state if the rate is out the
requested range. Calling clk_core_set_rate() with the closest rate
limit could solve the problem but:
- The underlying determine_rate() callback needs to account for this
  corner case (rounding within the range, if possible)
- if only round_rate() is available, we rely on luck unfortunately.

Fixes: 1c8e600440 ("clk: Add rate constraints to clocks")
Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171201215200.23523-11-jbrunet@baylibre.com
This commit is contained in:
Jerome Brunet 2017-12-01 22:52:00 +01:00 committed by Michael Turquette
parent 55e9b8b7b8
commit 6562fbcf3a
1 changed files with 33 additions and 4 deletions
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37
drivers/clk/clk.c
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@ -2000,6 +2000,7 @@ EXPORT_SYMBOL_GPL(clk_set_rate_exclusive);
int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)
{
int ret = 0;
unsigned long old_min, old_max, rate;
if (!clk)
return 0;
@ -2016,10 +2017,38 @@ int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)
if (clk->exclusive_count)
clk_core_rate_unprotect(clk->core);
if (min != clk->min_rate || max != clk->max_rate) {
clk->min_rate = min;
clk->max_rate = max;
ret = clk_core_set_rate_nolock(clk->core, clk->core->req_rate);
/* Save the current values in case we need to rollback the change */
old_min = clk->min_rate;
old_max = clk->max_rate;
clk->min_rate = min;
clk->max_rate = max;
rate = clk_core_get_rate_nolock(clk->core);
if (rate < min || rate > max) {
/*
* FIXME:
* We are in bit of trouble here, current rate is outside the
* the requested range. We are going try to request appropriate
* range boundary but there is a catch. It may fail for the
* usual reason (clock broken, clock protected, etc) but also
* because:
* - round_rate() was not favorable and fell on the wrong
* side of the boundary
* - the determine_rate() callback does not really check for
* this corner case when determining the rate
*/
if (rate < min)
rate = min;
else
rate = max;
ret = clk_core_set_rate_nolock(clk->core, rate);
if (ret) {
/* rollback the changes */
clk->min_rate = old_min;
clk->max_rate = old_max;
}
}
if (clk->exclusive_count)